<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        div{
            width: 50px;
            height: 50px;
            background-color: blueviolet;
            border-radius: 20px;
            margin: 0 auto;
        }


    </style>
</head>
<body>
        <!-- border-radius圆角 --> 
    <div></div>

    

</body>
</html>